Although it is admitted that a clear understanding of the phenomena of heredity would be of great value in solving many of the perplexing problems of evolution, yet our knowledge of these phenomena has increased but little during the last century. The processes of fertilization and development have been studied in great detail, but we have as yet no idea as to what is the essential agent in the transmission of the parental characters to the offspring. Scientists have, however, begun to study the outward facts of this transmission, and we are gradually beginning to see at least how we ought to go to work at these problems. Among the workers who have contributed most toward the establishment of definite laws of heredity Galton stands perhaps foremost; but there is one other worker of equal prominence whose papers, however, remained unknown to scientists for 35 years after their publication. This